Process for cracking hydrocarbon oils



F.' W. HALL El AL PROCESS FOR CRACKING HYDROCARBON OILS June 18, 1935.

Filed April 27. 1931 2 Sheets-Sheet 1 INVENTOR S June 18, 1935. F.'W.HALL ET AL PROCESS FOR CRACKING HYDROCARBON OILS Filed April 2'7, 1931 2Sheets-Sheet 2 INVENTORS J if Patented June 18, 1935 Frank W. HallandHarris A. Smith-Port Tex., assignors to The Texas Company,

Arthur, New

York, N. Y., a corporation of Delaware Application April 27, 1931,Serial No. 533,042

3 Claims.

This invention relates to an improved process and apparatus for theconversion oflhydrocarbon oil to produce gasoline or motor fuel and moreparticularly to a process wherein the oil is-com 5 mingled with hotvapors .previously subjected to cracking and the resulting mixture of:cracked vapors and vaporized charge is fractionated to produce adesirable gasoline fraction and a heavier liquid fractioncomposed ofpartially-converted oil and fresh oil for cracking in the vapor phase.

In its broadest aspect the invention Comprises a-process of convertinghydrocarbon oils to produce gasoline wherein a clean stock composed of amixture of partially converted oil and fresh oil which is free fromresidual and potential coke forming material is continuously evolvedandconducted in the form of vapor thru regenerative heating means whereinit undergoes cracking in the vapor phase. a l

The invention also contemplates an improved combination of apparatuswhich is particularly well adapted for carrying out the method of theinvention.

Our invention contemplates aprocess fortreating hydrocarbon oil for theproduction of gasoline wherein the oil which is to be cracked is heatedto a vaporizing temperature and the resulting vapors are ipassed .insuccession thru a series of regeneratively heatedconverters-wherein thevapors are brought into contact withhot refractory material arranged .inthe form of fines or checkerwork within the convertersand adapted toheat the vapors to a conversion temperature and maintain them" undercracking conditions during their continued passage thru the-successi-veconverters. The cracked, vaporsleaving the converters commingle withfresh incomingcharge to subject the vapors to partial condensation andeffectdistillation of the chargeoilso as to produce a combined vaporfree from residual ortarry matter and which is subjected tofractionationto form a gasoline vapor fraction and a heavier .liquid or refluxcondensate consisting of fresh oil .and partially converted oil which,.due to its freedom from heavy residual fractions, is adapted to form aclean circulating stock suitable forcirculating in a vaporous'c-onditionthru the converters and to undergo cracking therein without theproduction of substantial quantitiesof coke.

For our regenerative heating means we prefer to employ a plurality ofconverters somewhat similar to the regenerative heating stovesiused incarburetting watergas or-to the .typeusually employed in connection withblast. furnaces in steel mills. Thus, for example, when employingfourconverters, the converters are preferably interconnected in such amanner as to permit flowing vapors thru three of them in successionwhile the fourth is being heated up by blasting or firing until therefractory material has reached a temperature of 1409" F. or higher,following which the heated converter is out i nto the system and thecoolest converter cut out for reheating. Preferably the vapors areintroduced to the coolest converter still remaining in operation and arefinally discharged from the hottest or most recently heated converter.

When a cooled converter has been out out of the series for heating,

fuel gas may be admitted thereto to displace all the rich crackedhydrocarbon vapors remaining within the converter into suitablereceiving means after which combustion is initiated in the bottom of theconverter and continue therein until such time as the refractory materdesired temperature.

It has been customary in cracking hydrocarbon oils in ial has reachedthe the prior art when the vapor phase'to conduct the vaporized oil thrucontinuous tubular heating coils wherein the vaporized oil may *besubjected to relatively around 1200 F. for example. in tubes or coils inthis way high temperatures, Heating the vapors has been attended withconsiderable difiiculty particularly that of overheating of the tubes orpipes which must be exposed to relatively high furnace temperatures inorder to heat the vapors flowing thru the tubes to the desiredtemperatures.

Since the rate at which heat may be transferred from the walls of thetubes or pipes to the vaporous material flowing therethru isrelatively'low, the tube walls are therefore subject to relativelysevere heating which results in rapid deterioration of the metal andconsequently shortens the life of the tube or pipe in service. is thereadiness with which A further difficulty carbon is deposited on theinterior surfaces of the tubes particularly when the material 'flowingthru the tubes is not 'in-a completely vaporized state and thereforein-- "cludes particles of liquid which'when precipitated-against thehighly heated metallic surfaces are largely decomposed to form cokewhich adheres to the surface of the'metal and tends to I build up andform such a deposit that the tendency towards the overheating of thetubes is very greatly increased. For this reason it has been extremelyessential heretofore in this type of cracking operation to employ onlyrelatively light charging stocks such as kerosene and relativelylow'boilinggas oils. a

In our invention where-thevaporized oil is subjected to conversion in aseries of regenerative heating stoves or converters containing fines orcheckerwork formed from an inert or refractory heat retaining materialthe Vapors may be subjected to cracking temperatures for a prolongedperiod of time'without subjecting'the equipment to appreciabledeterioration from severe and extended heating. Such carbon as may beformed during the conversion deposits uponthe surfaces of the refractorymaterial and when the stoves. are successively cut out of service forreheatingthe deposited carbon is "readily and advantageously removed bycombustion during the reheating step during which the heat retainingmate:

Y rial during the, relatively short period of time that each converterremains on the line between reheatings, and this carbon deposit isreadily removed by combustion during the reheating step so thatnooperating delay is necessary to remove the carbon, and which is to becontrasted with the cracking of hydrocarbon vapors in a pipe coil heaterwhere it is necessary to shut down at quite frequent intervals in orderto manually remove the coke which has become deposited within the pipesor tubes. p

A further feature of our invention comprises continuously forming aclean circulating stock free from tarry or residual pitchy matter whichmight otherwise be readily decomposed to form substantial quantities ofcoke during passage of the oil thru the conversion zone. 3

These and'other objects and advantages of the inventionwill be betterunderstood from'the following description considered in connection withthe figures of the accompanying drawings which illustratediagrammatically a preferred form of apparatus for practicing theprocess of the invention. 7 V

In the drawings, Figure 1 is a diagrammatic elevational Viewillustrating apparatus adapted tothe carrying out of the process of the'invention.

Figure 2 is a diagrammatic view in plan illustrating a method ofinterconnecting the converters, V I

Referring to Figure 1, a pump 1 draws 011 from a source (not shown) andpumps the oil thru a line Lhaving a valve 3, leading to a reflux coil 4located in the upper portion of a fractionating column 5 and adapted tosupply cooling thereto. A by-pass 1, having avalve 3,is provided thruwhich oil not required to go thru the reflux cooling coil maybe passeddirectly into a pipe 6 leading from the outlet of the reflux coil 4 to aheat exchanger 9 thru which latter the 011 flows in indirect heatrelationship with a stream of residual oil being withdrawn from thesystem.

A by-pass pipe I 0 is also provided to permit bypassing the exchanger 9.From the exchanger}! the heated oil flows thru a pipe H leading to theupper portion of a stripping tower I2 into the interior of which it isintroduced thru a spray 13 adapted to distribute the oil over suitablepacking material M such as rocks, raschig rings, bubble trays,tiles andthe like.

Hydrocarbon vapors which have previously undergone cracking as willpresently be described which is withdrawn thru pipe 38 leading to thefirst of are introduced to a lower portion oi the stripping tower I2thru a transfer line l5, after flowing either totally or in part thruacoil l6 located in the bottom of the strippingtower and adapted tosupply heat for reboiling the liquid collecting in the bottom of thetower. The cracked vapors in passing upwardly thru thev packing materiall4 come into intimate and direct contact with the downwardly flowingcharge oil thereby cool- 7 ing and partially condensing the vapors andvaporizing the bulk of the charge oil. The liquid collecting'in thebottom of the stripping tower l2 which is composed of the unvaporizedresidual portions of the charge and tarry material condensed out of thecracked vapors is withdrawn thru a pipev l1, having a valve l8, to theheat eX changer 9 in which it is cooled while imparting its sensibleheat to the incoming charge. A portion of. the liquid being withdrawnthru the pipe I! may be conducted thru a pipe I9, having a valve 20,leading. to a coil 2| placed in the bottom of the fractionator reboilingthe liquid condensate collecting in the bottom of the fractionator andthereby facilitate fractionation within the tower. The oil leaving thecoil 2| is preferably returned thru a pipe 22 to the heat exchanger 9from which it may be withdrawn and disposed of as may be desired.

The vapor mixture rising to the top ofthe stripping tower I 2 isconducted thru a pipe 23 to the middle portion of the fractionator 5wherein it is subjected to fractionation to form avapor fraction,consisting of gasoline and fixed gases, and a relatively higher boilingliquid fraction collecting as a reflux condensate in the bot- I. tom ofthe fractionator.

The gasoline vapor is withdrawn from the top of. the fractionator 5 thrua pipe 24 leading to a condenser 25 wherein it is cooled and condensedto form a distillate accumulator or receiving drum 21 wherein thenon-condensable fixed or dry gases are separated from the gasolineliquid to be withdrawn thru a pipe 28 while the gasoline liquid may bewithdrawn thru a pipe 29 to storage or for further treatment.

The surplus reflux condensate collecting'in the bottom ofthefractionator 5 and which is composed of the fresh gas oil portion ofthe charge in admixture with clean circulating stock for vapor phasecracking, is withdrawn thru a. pipe 30 and conducted 'by means of a pump3| thru a line 32 leading to a pipe coil 33, in a suitable furnace 34,and wherein 1- 'the stock is heated to a vaporizing temperature,

preferably under superatmospheric pressure.

The heated-oil is discharged from the' heating .coil' thru a pipe 35,having a'valve .36,*into a vaporizing chamber 31 preferably'maintainedat a pressure lower than that maintained in the neating coil. Uponintroduction to the vaporizer the heated material is substantiallyentirely a series of concollecting in the thru a pipe 40,

porized oil is admixed'with incoming charge and;

returned to'the system for further treatment.

If desired, this unvaporized oil maybe conducted thru a pipe 44, havinga valve 45, leading to an atomizer or jet nozzle 46 interposed in the 5adapted to supply heat fora pipe 26 leadingto an the partially convertedoil ,manifold 69 thru the pipe 6|.

aor ztcv-s vapor line 38. 1 The velocity of the vapors flowing thru theatomizer 45 may be sufliciently high to'entrain the'liquid, which isusually relatively small in amount, and convert it to a mist of finelydividedform.,

The vaporized oil enters the lower portion or combustion chamber 41 ofthe first converter and flows upwardlythrua flue 48 to the top of theconverter from which point the vapors pass downwardly thru highly heatedcheckerwork material 49 and as a result of intimate contact with thisrefractory material the vaporsare heated to a suitable crackingtemperature. From the bottom of the checkerwork the vapors are passedthru a pipe 52 to the inlet of the next succeeding converter; From thebottom of the last converter the cracked vapors are passed into thetransfer line I5, already mentioned, and which leads to a mid pointofthe stripping tower l2.

Referring to Figure 2, the vaporized oil flowing thru the pipe 38 isconducted to a manifold 60 with branch pipes 61, 62, 63 and 54, eachhaving a .valve65, leading to the pipes 5|; 52, 53 and 54, each having avalve 55, interconnecting the four converters 390 39b, etc. Vapordischarge lines 56, 51,-58 and 69, each having avalve HI, connectingwith the pipes 5!, 52, etc. form. vapor outlets for each converterleading to a main vapor line H from which the vapor stream is conductedthru the transfer pipe !5 to the stripping-tower as. already described.Purging out pipes I2, 13, 14 and 15, each having a valve 15, areprovided thru which vapor remaining in any stove aftervit has been cutout of the system for reheating maybe displaced to a suitable gasometerTl in which the heavier portions of the vapor may condense and bewithdrawn therefrom thru a pipe 18 for subsequent return to the system.The uncondensed gaseous material remaining in the gasometer is availableas fuel gas for combustion purposes during the reheating operation andwhich gas is'conducted thru a pipe 19 leading to fuel gas inlets orburners 85 provided with air inlets 8|, and extending into thecombustion chambers 41 of each of the converters. When operating withfour converters as illustrated in the diagram. and where the vapors areflowing thru three of the converters in succession while thefourth isbeing reheated, the vapors may, for v example, enter the combustionchamber 41 of the coolest converter 39a from the After passing downwardthruv the checkerwork in this converter the vapors pass thru theconnectingpipe 52. to the combustion chamber of the next succeeding andhotter converter 39b and from which, after passing therethru, they flowthru the pipe 53 to the third and hottest converter 39c from which thecracked vapors are then passed thru the pipe 58, leading from the pipe54, and are conducted into the main vapor line H leading to thetransferline l5. .The converter39cl may be segregated or isolated fromthe series in order to "undergo reheating by closing the valves 65 and55 in the pipes 64 and 54, respectively, and" also closing the valves 55and Hi inthe pipes 5| and 69, respectively. At the time of segregatingit from the rest'of the converters it will, of course, be filled withpartially converted vaporized material and uponcutting it out of thesystem'these rich hydrocarbon'vapors may be displaced from the converterby introducing fuel gas, or preferably the fixed'or dry gases whichhavebeengenerated der pressure from the pipe 28 leading from theaccumulatordrum 2'5, thru the pipe'lfl and the burner 80 to thecombustion chamber of the converter. checkerwork displace the richerhydrocarbon va pors thru the pipe. leading to the gasometer As soon asthese rich vapors have been substantially completely displaced from theconverter the necessary amount of air may thenbe introduced thru theburner extending into the combustion space of the converter andcombustion of the entering dry gas. initiated. The supply of air may beregulated so as to substantially confine the flame to the combustionchamber and from which the hot products of combustion pass, upwardlythru the interior flue 43 and then pass downwardly thru and over thecheckerwork to heat it up, the period of combustion being prolonged fora sufficient time, preferably for not over an hour, to heat up therefractory material to the desired temperature which will usually rangefrom aboutl300 to 1400? F; The hot flue gas leaving the converter duringthe reheating step may be discharged into a flue 82 leading to a stack83'thru which it may be discharged to the atmosphere, although advantagemay be taken of its sensible heat content by returning a portion of thehot flue gas by meansof a fan 84 thru a :pipe 85 to the furnace 34.

When the refractory material has attained the desired temperature theflow of air to the burner 80 may be topped thus extinguishing the flameand terminating combustionv whereupon the valve 55 in the pipe 54 andthe valve 55 in the pipe 54 may be opened and also the valve 10 in thepipe 58 closed allowing the hot vapors from the converter 390 to enterthe newly heatedcone The fixed gases in flowing thru the 1 1n theprocess and which may be withdrawn un- I verter 39d and pass therethruinto the pipe 69 tem and reheated in a manner similar to that.

just described;

In the practice of our invention a charge stock,

which may comprise crude oil, after being pre- 7 heated during passagethru the reflux coil 4 and the heat exchangerv 9, is introduced to thestripping tower l2 wherein it is commingled with a stream of vaporspreviously subjected to cracking in order to condense undesirable tarryconstituents out of the vapors as well as to effect distillation of thesubstantial bulk of the crude. The tarry matter condensed out of thecracked vapors together with'the residual portion of the crudecollecting in the bottom of the stripping tower I2 may be withdrawn fromthe system as a fuel oilor to be used in any other desirable manner. i

The resulting vapor mixture comprising the partially cooled crackedvapors and the natural gasoline and gas oil fractions of the crudecharge is introduced thru the pipe 23 to the fractionator 5 wherein itis subjected to fractionation to form a'vapor fraction-composed of thenatural gasoline constituents of the charge and those fracto theaccumulator drum 2! wherein the fixed gases are separated from thegasoline. distillate. That portion'of the crude charge-exclusive of itsnatural gasoline constituents and comprising fresh gas oil which iscondensed in the fractionator 5 together with the relatively highboiling and partially converted portions of the cracked vapors, iswithdrawn thru the pipe 30 and pumped thru the pipe 32 to the heatingcoil '33 wherein it is heated to temperatures of around 700 F. or higherand preferably under pressureswhich may range from somewhat aboveatmospheric to 400 or 500 pounds or even higher. The heated oil isexpanded thru .the valve 36 into the vaporizing chamber 31 which may bemaintained at a pressure substantially lower than that within theheating coil in order to facilitate substantially entirelycompletevaporization of the heated oil. It is" contemplated that the conditionsof temperature and pressure may be'regulated to whatever extent isnecessary in order to effect substantially complete vaporization uponintroduction to the vaporizing chamber.

It is desirable to introduce the hydrocarbon oil to the converters in acompletely vaporized condition since when substantial amounts of :liquidin the form of droplets or particles are introduced to theconversionzone wherein the particles come into contact with the refractorymaterial a rapid decomposition of .the liquid particles may take placewith the production of substantial amounts of coke. The decomposition ofliquid into coke under these conditions is believed to take place to amaterially greater extent than is the case with oil which is, entirelyin the form of vapor or as a fine mist.

While the vaporizing oil mayin many cases be introduced directly fromthe coil outlet to the first converter which is under sufficiently lowerpressure than the heating coil to result in sufliciently completevaporization of the oil upon its introduction to the converter, meanshave been provided to facilitate separation of liquidparticles from thevapor prior to its entry tothe conversion zone. This unvaporizedmaterial may be Withdrawn from the bottom of the vaporizing chamber andbe either admixed with the fresh charge entering the system or passed--thru the atomizing means 46 wherein advantage may be taken of theatomizing effect of vapors flowing thru the atomizer at a high velocityto convert this liquid, which under ordinary conditions, is ofrelatively small amount, to a sufficiently fine state of division suchthat its introduction to the converters is not attended with asubstantial amount of decomposition to form coke or carbon.

The vaporized oil may enter the first converter of the seriesat atemperature of from 700 to 800 F. and in passing thru the heatedcheckerwork of this converter may be heated tofrom 900 to 1000 F. Fromthis converter it' fiows'thru the second or intermediate and nexthottest: converter of the series wherein the vapors may'be heated tofrom l000 to ll00 F.' while in the third andhottest converter they maybe raised to a temperature of from 1100 to 1300 F. The degree andfrequency of reheating of'the converters may be regulated so that thetemperature of the vapors finally leaving the conversion zone may beconsistently around 1200? a F., although higher temperatures may readilybe maintained merely 2,005,670 I converters: arranged in seriesthetemperature of the vapor leaving the last converter may be maintainedsubstantially uniform withoutmaterial .the vapors are subjected to asubstantial period of digestion at high temperatures when fiowin'g thruthe series of three or more converters in succession, which extendedtimeof digestion is desirable from the standpoint of extending thedegree of the conversion reaction, that is, to increase the amount ofcracking with the consequent production of larger yields of gasoline orIt is contemplated that'any desired pressure may beemployed and that auniform pressure may be maintained throughout the entire system,although ordinarily it may prove more desirable to maintainthe heatingcoil or pipestill under superatmospheric pressure,'releasing thepressure somewhat in thevaporizing chamber, maintaining a, reducedsuperatmosphericpressure in the converters,,and reducing the pressurestill further, or to approximately atmospheric pressure in thedephlegmating means;

, Obviously many modifications'and variations of the invention, ashereinbefore set forth, may be made without departing from'the spiritand scope thereof, and therefore, only suchnlimitations should beimposed as areindicated in the appended claims. 7 V '7 We'claim: t

1. The process of treating hydrocarbon oil which comprises passing aclean relatively heavy oil through a heating zone wherein it is raisedto a vaporizing.temperatura'separating the resulting heated oilinto'vapors and a liquid residue, passing saidfvapors, through aconverter zone in contact with highly preheated solid re fractorymaterial wherein said vapors are raised to a cracking temperaturecontrolled independently of said vaporizing temperature and aresubjected to'conversion by the contained heat of said preheatedrefractory material, removing resulting cracked products and introducingthem into a separating zone wherein vapors separate from liquid residue,removing vapors from the separating zone and passing them directly intoa fractionating zone independent of said heat variations therein due toperiodically cuttingout one converter for reheating and cutting into-theseries a newly reheated converter." Furthermore,

andv passing it through said heating zone as said clean oil firstmentioned and introducing fresh relatively heavy charging stock intosaid separating zone in contact with the introduced cracked products tocause at least'partial'vapon ization of said charging stock, andremoving liq- I uid residue from said separatingzone.

2. A process in accordance with claim l wherein liquid residue leftafter separating vapors from the heated clean oil removed from theheating zone, is introduced into said separating zone in contact withthe hot cracked products intro- 5 duced thereinto from the converterzone.

3. A process in accordance with claim 1 wherein liquid residue leftafter the separation of.

vapors from the heated clean oil removed from the heating zone isintroduced in mist form into said converter zone.

